Timer lag

[Fredsie]

Hi

I have a simple gas heating system controlled by a programmable timer (Honeywell CM67NG). This generally works fine, but seems to suffer from control delays.

As expected, once the required room temperature is reached, the boiler shuts off. After a while as the room temperature drops, the timer display shows the "demand" indicator to re-heat the room. However despite the demand indication, the boiler does not come on immediately. It can sometimes take 20 or 25 minutes before it fires up.

I guess maybe the timer is trying to avoid "hunting" around the set temperature, but frankly when the demand indication is on I want the boiler/pump to be on.

I can't find any way in the settings to alter this (I know I can affect the lag in shutting off somewhat with the "minimum on" time.)

Do all timers do this? If not, can anyone suggest one that doesn't?

Many thanks

Fred

[SensibleHeatUK]

If your CM67 is the wireless model and connects to a HC60NG then there are parameters you can set for the HC60NG for the number of starts per hour - if this is set to a very low number (say 2 starts per hour) then that could be the cause of the delay.

You should check to see if the green light is on the HC60NG, if it is but the boiler is not firing then it may be the boiler causing the delayed start. If this is the case then you'll need to see if there are any control parameters that can be adjusted on the boiler to improve its response.

[Fredsie]

Hi

Thanks for the quick response!

There's no model number on the outside of the receiver but it does look very like the pictures of the HC60NG on the web.

I've just checked and although currently the demand indicator is on, the green light on the receiver is off. If I nudge up the temperature setting on the transmitter a couple of degrees it comes on immediately, as does the boiler.

So it seems the delay's down to a combination of the sender/receiver rather than the boiler. You mention settings on the receiver but I can't find the instructions anywhere on how to make such adjustments. If anyone could point me to the manual, I'll see what difference the settings make.

Cheers

Fred

[jwxfs]

Hi

Thanks for the quick response!

There's no model number on the outside of the receiver but it does look very like the pictures of the HC60NG on the web.

I've just checked and although currently the demand indicator is on, the green light on the receiver is off. If I nudge up the temperature setting on the transmitter a couple of degrees it comes on immediately, as does the boiler.

So it seems the delay's down to a combination of the sender/receiver rather than the boiler. You mention settings on the receiver but I can't find the instructions anywhere on how to make such adjustments. If anyone could point me to the manual, I'll see what difference the settings make.

Cheers

Fred

Try here:

http://products.ecc.emea.honeywell.com/europe/ecatdata/pg_evohome.html

Regards

Jason

[Fredsie]

Yes thanks Jason, I did start at the Honeywell site and spent some time looking though these, but I couldn't find what the original responder mentioned - settings specifically on the HC60NG. In fact looking at it it seems unlikely there's any way to actually make setting changes to it directly. If its settings can be changed via the timer unit then I have the instructions for that, but there's no "max number of times on in an hour" or anything like that.

[SensibleHeatUK]

The CM67 does allow access to parameters that affect how the HC60NG operates - I don't think it changes anything in the HC60NG but rather changes how the CM67 sends demands.

You'll need to put you CM67 into installer mode then look for the "cycles per hour" and "minimum run time" to change the required settings. Unfortunately I don't remember how to put the CM67 into installer mode as it is about 5 years since I last had to work on one. If Google does not help then you could phone the Honeywell helpline to see if they can email over a copy of the installer guide.

[Fredsie]

I have no problem doing that, I still have the original Installer Instructions for the CM67. It was the instructions for the HC60 that I thought I was looking for. But that makes much more sense.

The Installer Setup has the following settings:

1: AM/PM 24hr select
2: Reset time/temp program
3: Minimum on time
4: Accessory Module type
5: Heat/cool operation
6: Not used
7: Pump exercise feature enable
8:Cycle rate
9: System synchroniser
10: Upper setpoint limit adjust
11: Lower setpoint limit adjust
12: Measurement offset adjust (temp)
13: Not used
14: Prop band width
15: Optimisation enable
16: Loss of Communications Instruction
17: reset Installer Mode Parameters to defaults.

That's all you get. I can't see that any of these do what I'm looking for.

Cheers

Fred

I can of course provide the allowed settings and notes for any of these that sound promising.

[SensibleHeatUK]

I have no problem doing that, I still have the original Installer Instructions for the CM67. It was the instructions for the HC60 that I thought I was looking for. But that makes much more sense.

The Installer Setup has the following settings:

1: AM/PM 24hr select
2: Reset time/temp program
3: Minimum on time
4: Accessory Module type
5: Heat/cool operation
6: Not used
7: Pump exercise feature enable
8:Cycle rate
9: System synchroniser
10: Upper setpoint limit adjust
11: Lower setpoint limit adjust
12: Measurement offset adjust (temp)
13: Not used
14: Prop band width
15: Optimisation enable
16: Loss of Communications Instruction
17: reset Installer Mode Parameters to defaults.

That's all you get. I can't see that any of these do what I'm looking for.

Cheers

Frede

Cycle Rate should be the number of starts per hour, and you might want to change the minimum on time if it is very short - the standard default is 1 minute which is too short to achieve very much so a higher value would be better (3-5 minutes depending on how big the boiler is should be fine).

[Fredsie]

That's good, thanks.

The Minimum On time was set to 5, which is the maximum. (The range is 1 to 5 mins, which seems pretty useless to me, a minimum on of 15 mins makes much more sense. When is say a 1 minute minimum on time ever going to have any effect?)

The Cycle rate was set to 6 cph, which seems reasonable. However I've pushed it up to 12 to see if that will affect the issue.

Cheers

[Fredsie]

Well this hasn't made any difference. The thermostat sits with the "demand" signal showing but does not fire the boiler.

In fact this is what happens.

1. Thermostat set to 21C. Actual room temp 21C, all fine.
2. Room temp drops to 20.5C, demand indicator comes on, but no boiler.
3. 30 mins later, room temp drops to 20.0C, demand indicator still on, still no boiler.
4. Another 15 mins, room temp drops to 19.7C, boiler kicks in, and stays on until 21C reached.

So the room temp needs to be 1.3 degrees below the target temp for the system to fire. I'm sure this is deliberate, but it's not adjustable and I don't like it.

So I guess I'm back to my original question, does anyone know of a control system that doesn't do this? At least with the old electro-mechanical timers connected to a separate thermostat, it did what it was told!

[SensibleHeatUK]

Well this hasn't made any difference. The thermostat sits with the "demand" signal showing but does not fire the boiler.

In fact this is what happens.

1. Thermostat set to 21C. Actual room temp 21C, all fine.
2. Room temp drops to 20.5C, demand indicator comes on, but no boiler.
3. 30 mins later, room temp drops to 20.0C, demand indicator still on, still no boiler.
4. Another 15 mins, room temp drops to 19.7C, boiler kicks in, and stays on until 21C reached.

So the room temp needs to be 1.3 degrees below the target temp for the system to fire. I'm sure this is deliberate, but it's not adjustable and I don't like it.

So I guess I'm back to my original question, does anyone know of a control system that doesn't do this? At least with the old electro-mechanical timers connected to a separate thermostat, it did what it was told!

That does sound very odd! Cannot suggest much more you can do unless there is someone technical at Honeywell who can check more settings with you.

If you do decide to "upgrade" then the Evo Touch is a much more polished system compared to the CM67RF, and it has much more flexibility if you decide to go down the route of upgrading to additional zones later. The downside is it is much more expensive than the older CM controllers (although it does come with a BRD91 boiler relay which is an update to the HC60NG).

[jwxfs]

Going back to your original post you should shop around Programmable Wireless Thermostats.

If you have a modern boiler that prevent too rapid recycling then a basic one should be fine or you could look at the Siemens REV200 RF. This allow a straight 2 position on / off mode with 0.5c temperature differential. Personally I would go for the PID 6 setting with a 6 minute cycle time to be safe.

https://www.siemens.be/cmc/upload/cms/docs/sbt/hvac/Brochures_Datasheets_manuals/FR/01_Thermostats/Datasheets/N2214_REV200RF_EN.pdf

[Fredsie]

Thanks guys, I'll have a look at them.

All seems to come down to the temp differential in the end - the system clearly expects a 1.5 degree drop before it'll kick in. The demand indicator just misleads.
They could fix this by:
- allowing you to tweak the switching temp difference, say 0.5 to 2.0 in half degree steps (I see that some stats let you do this)
- not turning on the demand indicator until it's really ready to turn on the boiler.
Easy really!

[IM35461]

Hi you may wish to try tweaking 14:PB which is the differential that the temperature has to drop before it starts heating again.

The default I think is 1.5

[Fredsie]

You're dead right - that is the one I want to adjust, and the default is 1.5.
Clearly I would need it to be smaller than that, but for some reason they've decided the adjustment range should be 1.5 to 3.0, in steps of 0.1. So I can't reduce it from the default.